/ Thesaurus / G Synonyms of gear box Find synonyms for: Noun1. gearbox, gear box, gear case, shell, case, casingusage: the shell (metal casing) in which a train of gears is sealedWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: apogee Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language